We have a 14 seer downstairs (d/s) unit and a 13 seer up stairs (u/s) unit on our house. The d/s is where we live as the u/s we only use for the game room and extra room as an office. So we "live" (no one sleeps upstairs) down stairs and therefore don't have to cool the u/s as much as the down. The d/s keeps much cooler as the heat rises to the second floor so we don't run the up a/c as much. I know heat rises, but should I keep the up stairs at some level so the d/s unit does not have to cool as much. I just don't know how much the heat building upstairs impacts the down stairs cooling. Is it better to let the d/s unit cool as needed and keep the u/s at a higher level (90?) or lower like 82 if we try to keep the d/s closer to 76 when we are here. I do have programmble thermostats. I am trying some tests to see, but am curious for feedback from the forum.

Here are some details that may be helpful. Right now the outside is 95 in mid afternoon (3:45pm) heat. DS temp is 77 degrees (a/c has not been all day) u/s temp is 88 (a/c was on about 5 minutes then I jumped it up to 90 on the thermo before it should kick on. Looking for the best and most cost effective solution. :)

Run the upstairs unit more cold air falls.

What size units do you have??

I think the d/s is a 5 ton and upstairs is a 2.5 ton.. So you suggest keeping the upstairs running more to equalize or let the cooler air fall?

Yes I would, the more you run the upstairs the less the downstairs will kick on. Plus by not running the upstairs unit. All the hot air has no place to go. The other option would be to put a door or curtain at the top of your steps and only use 1 floor.